Starting from a brief review on the concepts of electrical resistance and impedance and the definition of thermal resistance, it is shown how thermal impedance can be defined from a simple situation of an ideal semi-infinite solid sample subjected to uniform sinusoidal heating at its surface. Using the thermal impedance definition, the non-stationary component of the temperature field perpendicular to the surface of the sample can be rewritten in a more compact form than as usual. It is shown that a dimensionless number dependent on thermal impedance can be defined for non-stationary phenomena to compare the efficiency between the different modes of heat transfer. The thermal impedance concept for the little-known for most people (but not least important) case of non-Fourier heat conduction is also discussed here. We show that the thermal impedance for diffusive Fourier heat transfer is a complex valued parameter with the same real and imaginary parts. However, this behavior is affected when approaching non-Fourier conditions, under which the imaginary component can become a pure imaginary parameter. These topics are not treated in heat transfer and physics textbooks. However, the subject can be of interest not only for students and teachers at undergraduate and graduate levels but also for scientists dealing with heat transfer in the presence of time-varying periodical heat sources.

从对电阻和阻抗的概念以及热阻的定义的简要回顾开始，展示了如何从理想的半无限固体样品在其表面受到均匀正弦加热的简单情况来定义热阻抗。使用热阻抗定义，垂直于样品表面的温度场的非平稳分量可以比通常更紧凑的形式重写。结果表明，可以为非平稳现象定义依赖于热阻抗的无量纲数，以比较不同传热模式之间的效率。此处还讨论了大多数人鲜为人知（但并非最不重要）的非傅立叶热传导情况的热阻抗概念。我们表明，扩散傅立叶传热的热阻抗是一个复值参数，具有相同的实部和虚部。然而，当接近非傅立叶条件时，这种行为会受到影响，在这种条件下，虚部可以成为纯虚参数。这些主题在传热和物理教科书中没有涉及。然而，该主题不仅对本科生和研究生水平的学生和教师感兴趣，而且对在时变周期性热源存在下处理热传递的科学家也很感兴趣。这些主题在传热和物理教科书中没有涉及。然而，该主题不仅对本科生和研究生水平的学生和教师感兴趣，而且对在时变周期性热源存在下处理热传递的科学家也很感兴趣。这些主题在传热和物理教科书中没有涉及。然而，该主题不仅对本科生和研究生水平的学生和教师感兴趣，而且对在时变周期性热源存在下处理热传递的科学家也很感兴趣。